The present invention relates to an image forming apparatus such as electrostatic copying machine, facsimile, laser beam printer or the like. More particularly, the present invention relates to an image forming apparatus equipped with an organic photosensitive material drum having good wear resistance and a cleaning means having an elastic blade, which causes neither “dash mark”, “toner filming”, “blade squeaking”, nor “blade turning-over”, and also has “long lifetime”.
In the image forming apparatus described above, an electrophotosensitive material is used in the step of repeating a charging means, an exposing means, a developing means, a transferring means and a cleaning means in the image forming process. A latent image formed by the charging means and the exposing means is developed with a toner as powders in the form of fine particles. Although the developed toner is transferred onto a transfer material such as paper in the transferring means, the whole toner (100%) is not transferred and a portion of the toner is remained on the surface of the photosensitive material. When the residual toner is not removed, a high-grade image free from contamination can not be obtained in the repeating process. Therefore, cleaning of the residual toner is required. Transfer papers set in the paper feeding portion such as paper feeding cassette are sent to a transfer paper transporting path through paper feeding rollers and then transported toward an image forming portion through transportating roller and resist rollers arranged on the transfer paper transporting path, where an image is formed.
Typical examples of the cleaning means include those using a far brush, a magnetic brush, an elastic blade or the like. In view of the cleaning accuracy and rationalization of the constitution of the apparatus, a cleaning means for cleaning by directly contacting a blade-shaped resin plate with a photosensitive material using an elastic blade is generally selected.
In the image forming apparatus described above, various photosensitive materials having sensitivity at a wavelength range of a light source used in the apparatus are used. One of them is an inorganic photosensitive material using an inorganic material such as selenium in a photosensitive layer and the other is an organic photosensitive material (OPC) using an organic photosensitive material in a photosensitive layer. Among these photosensitive materials, the organic photosensitive material has widely been developed because of its easy production, wide range of choice of photosensitive materials such as electric charge transferring material, electric charge generating material and binder resin, and high functional design freedom as compared with the inorganic photosensitive material.
The organic photosensitive material includes, for example, a so-called multi-layer type photosensitive material having a multi-layer structure comprising an electric charge generating layer containing an electric charge generating material and an electric charge transferring layer containing an electric charge transferring material, and a so-called single-layer type photosensitive material wherein an electric charge generating material and an electric charge transferring material are dispersed in a single photosensitive layer. Among these photosensitive materials, the multi-layer type photosensitive material widely controls a market.
The single-layer type photosensitive material has attracted special interest recently since it has advantages that the productivity is excellent because of simple layer constitution, film defects of the photosensitive layer can be prevented from occurring because of less interfaces between layers, and one photosensitive material can be used in positively and negatively charging types by using an electron transferring material in combination with a hole transferring material as the electric charge transferring material.
As described above, the cleaning means using the elastic blade removes the residual toner on the surface of the organic photosensitive material by contacting the blade-shaped resin plate with the surface of the organic photosensitive material. It has been known that, when a force of press-contacting the elastic blade with the surface of the organic photosensitive material (linear pressure of blade) or an angle between the elastic blade to be contacted with the surface of the organic photosensitive material (press-contact angle of blade) is small, the residual toner passes through a microspace between the elastic blade with the surface of the organic photosensitive material in the pressed state and is fused strongly on the surface of the organic photosensitive material in the state where toner particles are collapsed, thereby to cause phenomena referred to as “dash mark” and “toner filming”, and that optical attenuation does not occur because light is screened, thereby to cause image defects.
One of significant causes for dash mark and toner filming includes, for example, paper powders produced from the transfer paper. In case the transfer paper passes through various transporting rollers such as paper feeding rollers and resist rollers, paper powders are produced by friction with the rollers.
Fillers such as talc contained in the paper powders are negatively charged. In a reversal development type image forming apparatus using a positively charging single-layer type photosensitive material, since a negative bias is applied in the transferring portion, the paper powders are liable to be separated from the transfer paper and are attracted to the surface of the positively charged single-layer type photosensitive material by an electrostatic attraction. The paper powders adhered are adhered or fused on the surface of the photosensitive material more strongly by sliding friction of the blade and function as an inducer for dash mark and toner filming.
To improve the cleaning performance, thereby to prevent dash mark and toner filming from occurring, when the linear pressure or press-contact angle of the blade is enhanced, there sometimes arise a phenomenon referred to as “blade squeaking” wherein the elastic blade causes resonance sound on sliding friction of the surface of the organic photosensitive material, and a phenomenon referred to as “blade turning-over” wherein the blade deforms in waves or rotates in the same rotation direction as that of the drum.
In case a mechanical load on the surface of the organic photosensitive material increases and the wear amount of the photosensitive layer increases, problems such as lowering of chargeability and sensitivity occurs at an early stage, thereby making it difficult to obtain a high-grade image, and thus a so-called “long-lifetime” image forming apparatus can not be obtained.
An object of the present invention is to provide an image forming apparatus equipped with an organic photosensitive material drum as an image carrier and a cleaning means having an elastic blade, which causes neither “dash mark”, “toner filming”, “blade squeaking”, nor “blade turning-over”, and also has “long lifetime”. Another object of the present invention is to specify a binder resin structure of the organic photosensitive material drum, thereby achieving longer lifetime of the image forming apparatus.